Signaling system



April 10, 1928.

F. J. SINGER SIGNALING SYSTEM Filed April 2 27 2 Sheets-Sheet 1 IN V EN TOR. EJ Sayer ATTORNEY April 10, 1928.

F. J. SINGER SIGNALING SYSTEM Filed April 2, 1927 2 Sheets-Sheet 2 fix IN VEN TOR. Z'J Sz'gyer BY g A TTORNEYS.

Patented Apr. 10, 1928.

UNITED STATES PATENT. OFFICE.

FRED J. SINGER, OF BROOKLYN, NEW YORK, ASSIGIFOR TO AMERICAN TELEPHONE m TELEGRAPH COMPANY, A CORPORATION OF N EW YORK.

SIGNALING SYSTEM.

Application filed a ru 2, 1927. Serial 110,180,521.

This invention relates to multi lex signaling systems, and more particular yto multiously employed for the transmission of sig nals.

The invention comprises a system inwhich multiplex transmission is a plied to a circuit of the four-wire type, t at is, a circuit in which one transmission line is used for transmission in one direction and another transmission line 'is used for transmission in the opposite direction.

Th1s invention further comprises a signaling system in which signals from a pmrality of signaling sources or stations may be simultaneously transmitted in one direction to a plurality of'distant stations'over a common signaling path while signals from distant sources or stations may be simultaneously transmitted over another signaling path in the opposite direction.

This inventlon further comprises a signaling system in which a plurality -of oscillators of successive odd harmonics of a fundamental frequency are simultaneously modulated by low frequency signals from various low frequency signaling sources, and

in which the modulated currents are again modulated upon a plurality of other sucessive harmonics, preferably even harmonics of the same fundamental frequenc By employing odd and even harmonics or the oscillators used in modulation, any harmonic products introduced into the circuits by loading coils, transformers and the like will be greatly prevented from causing troublesome interference.

A four-wire arrangement is advantageous where it is desired to apply to lines currents of the same frequencies for transmission in both directions and particularly so when these-lines are constructed entirelyof cable.

.' In this application, two of.the wires will be for transmission in one direction employe and the other two of the wires will be used for transmission in the opposite direction. Accordingly, amplifiers may be interposed which introduce greater gains than those which may be interposed in a two-wire circuit. Moreover, the am lifiers required in an arrangement of the our-wire type may be separated by greater distances than sim1-' lar amplifiers may be separated in a two- I wire circuit. Furthermore, the four-wire circuit avoids the high degree of ca acity balance re uired between two wire cab e circuits for t e transmission of currents of the same frelml uencies. Whatever capacity balance wo d be re uired in a four-wlre circuit may be considerably reduced by ouping together respectively the east an west bound circuits, and electricall separating the groups by choosing non-ad'acent pairs of conductors in the cable, by s 'elding the two groups of conductors, by employing separate cables for the two groups, etc. The methods of separation form no part of this invention, however, and need not be de- 10 scribed herein for these are already well known to those skilled in the art.

While this invention will be pointed out with particularit in the appended claims, the invention itse f, both as to its further objects and features, will be better understood, from the detailed description hereinafter following when read in connection with the accompanying'drawing, in which Fi e 1 represents one embodiment of the invention shown here-merely for the purpose of illustration, Fig. 2 shows curves illustratin the principles of this invention, and Flg. 3 "shows the use of directional transmitters and receivers to replace the four wires shown in Fig. 1 for transmission between various stations.

Referring to Fig. 1 of the drawing, a four-wire system is disclosed embodying apparatus shown herein as located at stations 00 A and B. Ordinary low frequency signaling lines capable of transmitting a com aratively wide band of frequencies, suc as lines ML and MIL are shown extending between stations A and B. 05

In order to provide for four-wire carrier transmission over the above mentioned lines, a common carrier transmitting circuit TL is interposed between the line ML, and the secondary winding of a-repeating coil R for substantially suppressing'the transmis- I05 sion of fr uencies lying outside of these limits. Suc apparatus are usually referred to as filters, the filters "connected to the primar winding of the repeating c011 R, be

pre erably band filters, designated by the-1m reference characters B,F, B F and- B F. These filters should preferably be of the broad band t e as disclosed in the patents to G. A. Cam gell, Nos. 1,227,113 and 1,227,- 114, dated Lizzy 22, 1917. Where it is desired to suppress oneo'f the side bands resulting from the modulation of a carrier current by asingle signaling current or by a group of signa ing currents, the filter connected to the circuit should be so designed as to transmit a band of frequencies extending either above or below the assigned carrier frequency by an amount substantially equal to the range of the frequency spectrum required by the signaling current or currents.

In a similar manner, a common carrier receiving. circuit BL is interposed between the main line ML 'and the primary winding of a repeating coil Rf. The secondary windingof the repeating coil R,' is concoil R and L,,'" aria to be and B F which are in all respects similar to the filtersjlB F, 3 F, and B F connected to the p ary winding of. the repeating L and-L L,"' and L,,,', L and L L and'L, L, and L and L and respectively, designate similar low uency signaling circuits, such as teleh or telephone circuits, in iroiips, 1, 2 1 10 L11 gra an 3, respectively. The lines L I1 and L, are to be used for the transfrequencies, preferably'oscillators of odd or 'of even harmonics of some fundamental frequenc are d ated b the reference characters O and In t he case under consideration let it be assumed thatthese oscillators sustain oscillations of different odd harmonics -of a definite fundamental freuency. The oscillator 0 is common to t e modulators M M and M and the oscillator O, is common to the modulators M M and M It will be obvious that the modulating arrangements hown herein are indicated merely1 schematically and may be organizations w ereby moderately high frequenc oscillations from any source may be modulated in accordance with lower fre quency signals, these modulating arrangements being preferably of any well known vacuum-tube type.

In order that the modulated carrier currents received at station. A from station B may be translated into the original low frequency signals, a plurality of demodulating arrangements are rovided, designated D1!!! D10]! Dlllll, D20!!! D211! and D These demodulating arrangements may also be of any well-known type, preferably of some well-known vacuum tube type. In the particular illustration of this application, the ordinary method of detection and demodulation 1s involved and no carrier current need be supplied. If, however, the carrier current and one side band were suppressed at station B by the band fi1ters'BF,, BF BF BF BF,," and BF,," in each respective case, the socalled homodyne method of detection or demodulation could then be employed, necessitating the application of a definite carrier frequency to each demodulating arrangement at the same time that the received modulated carrier wave were applied thereto. Accordingly, it would be necessary to connect to the demodulators shown at station A oscillators of the same frequencies as are used in modulation at the distant station. Therefore, to accomplish this purpose, an oscillator, such as 0,, could be connected in common to the demodulators D,, D,,"' and D and an oscillator, such as 0,, could be connected incom- I1x)1or 1 to the demodulators D D,,,". and

so -The out uts; of the modulators 'M,, M M M B1,, and M are impressed upon band filters BF,, BF BF BF BF and BF respectively, these band filters being adaptable to freely transmit either of the side bands resulting from modulation while substantially suppressin the'carrier frequency and the other side %and if the homodyne method of detection were employed. If the ordinary method of detection mentioned hereinabove were employed, however, the carrier wave and both side bands would be transmitted by these filters. illustration of this ap lication the latter method is involved and the carrier wave and both side bands resulting from modulation are freely transmitted and all other frequencies are substantially suppressed.

The currents impressed upon the'demodulators D1!!! D101", un! D20!9 D2!!! and D,,," are received from theband filters BFIIII, mr, BFHHI, !!!q M/n and BF,,.,", respectively, these band filters being. similar in all res ects to the band filters BF,, BF BF, F BF and BF, employed in transmitting the products of modulation. The transmitting channels TL,, TL and TL receive theuseful products of modulation after transmlssion through the band filters BF' and BF BF and BF and BF, and BF respec- In the particular tively. Similar receiving channels RL,, BL and RL, receive the moderately high frequency currents which are to be impressed upon the band filters BF,"' and BF,,,, BF,," and BF,,, and BF,, and BF,,, respectively, which are to become subsequently demodulated.

In order to translate the modulated currents of groups 2 and 3, which are im ressed u on the transmitting channels T 2 and T into still higher frequency modulated currents, modulator-amplifiers MA, and MA are provided, each modulator-amplifier including any well-known modulating arrangement for modulation and any wellknown amplifying arrangement for amplify ing the products of modulation. Oscillators -0,, and 0 are connected to the modulatoramplifiers MA and MA,,- r ectively, these oscillators being of any we l-known type,

' preferably of some vacuum tube type. These oscillators may sustain oscillations of any frequency, preferablycurrents of some definite odd or even harmonics of the-same funda; mental frequency common to oscillators 0;, and 0,. In the particular illustration of this application these oscillators may preferably sustain oscillations of even harmonics of the flmdamental frequency common to the oscillators 0,, and 0,. The products of modulation after amplification are trans mitted to the band filters.B,F. and B F, rc-

spectively, each of these band filters pref erably transmitting one of the side bands resulting from the latter modulation and substantially suppressing the carrier frequency, the other sideband and allother products of modulation.

Demodulator-amplifiers DA and DA are connected to the (receiving channels BL, and RL,, respectively, at station A. Inasmuch as the homodyne principle is involved throughout the illustrated case, the same frequencies that are impressed upon the mo ulator at the transmitting station in modulation are also 'im ressed upon the def modulators in demod ationl Accordingly,

the oscillators and 0,, are also connected to the demodulator-amplifiers DA and DA,, respectively, transmitting currents of the same frequencies that are used in modulation, to these demodulators, namely, currents of frequencies equal to those im ressed u on the modulator-amplifiers M 2 and A,, respectively, and which are preferably even harmonics of the same fundamental frequency which is common to the oscillators 'O, and 0,. The currents which are imressed upon the demodulator-am lifiers A and DA, at station A are receive from band filters B,F",and B,F"', respectively,

, these band filters being similar in all respects to the band filters B F and B,F which receive the products of modulation from the VA to station modulator-amplifiers MA and MA,, respectively.

' The currents transmitted by the band filters B,F, B,F and B,F are transmitted through the repeating coil 3,, through the main transmitting channel TL and through the main line ML, to the main receiving channel RL at station B and the repeating coil R, thereat. The apparatus at station B is similarin all respects to the apparatus at station A, similar reference characters being employed to designate similar parts, the reference characters designating apparatus at station B being differently primed, however.

It'will be apparent that the system just described is one in which the channels of transmission in one direction are confined to one pair of wires ML, in the four-wire circuit, and those of transmission in. the other direction to the other pair of wires ML the channels of transmission in eachdirection being divided into a number of groups (only threev of'which are shown), each group being subdivided into a finite number of channels, such as ten (only two of which are shown).

Group 1 is operated on the principle of sinrier wave, these'doubly modulated products being then transmitted to the distant station.

For the pifrpose of illustration one of the channels in group 1, i. e., the channel originating in line L,, willbe traced from station B. -An oscillator 0 of a definite fre uency, preferably of an odd harmonic of a fun amental frequency, is trasmitted to the modulator M,. Signals .coming in over line .L, also are impressed upon the modulator M,.

In the case of telegraphy, the modulator may comprise ,a relay controlled by a telegrap key, a printer or any other sending device, or, in general, it may be any other type of mods ulator well-known in the art which will cause the current of oscillator O, to become-modulated in. accordance with the signals coming in over the line L,. The products of modulower or t e upper side band, needbe transvlation pass through the filter BF,, this filter the line L,'.

mitted, while the carrier frequenc and the undesired side band may pre erab y be suppressed. After passing through the filter BF the modulated signals are transmitted through a transmitting channel TL to another band filter B B. which has a wider range of transmission inasmuch as it. must freely transmit not only the modulated currents transmitted by the band filter BF but also the modulated currents transmittedby the band filter BF and any other .modulated currents which. may be developed in the channels of group 1 and lie between definite limits of frequency. After passing the band filter B F the currents are transmitted through the-repeating coil R, at station A, then through the main transmission channel TL, over the main line ML to station B, where, after passing through the main receiving channel RL' and through the repeating coil. R the modulated currents are impressed upon a band filter B F, all extraneous currents being suppressed thereby. These modulated currents then pass through the band filter B F' through thd receiving channel RL through the band filter BF, to the demodulator or detector D so that the received modulated currents may be properly demodulated in order to derive the signals or1ginating at station A in line L,, these derived signals being received at station B in It will be understood that if the homodyne method of detection were employed, then the carrier current and one side band thereof would be suapressed. Current of an oscillator such as which sustains oscillations substantially equal in frequency to those sustained by the oscillator O at station A, mightfhen be transmittted to the demodulator D, for the purposes of demodulation. The band pass filters B F and B,F at station A and the bandfilters B F' and B F at station B are designed to have very high impedances for currents of all frequencles flowing between station A and station B lying in group 1. Similarly, the other band filters connected to the repeating coils mutually exclude all the frequencies of currents in neighboring groups, thereby permitting the currents in one group to flow over the corresponding and appropriate channel and main line to be received by the proper band filter at the receiving station.

It will be apparent that the channels of group 1 operate on the principle of single modulation and that,.in the case of telegraphy, it is possible and perhaps desirable to transm't the carrier along with both side hands over the main line. The channels within groups 2 and 3 o erate on the principle of double modulation, and the transt.

, mission of current through one of these channels" will now also beconsidered in some detail.

The oscillator 0 similarly sup lies current to the modulator M to mo ulate the signals coming in over the line L In a telegra h system, the side bands of the current 0 oscillator 0 may be transmitted along with the carrier current, the band filter BF suppressing extraneous currents and currents of neighboring channels which would ordinaril tend to interfere with the faithful transmission of signals. The output of the band filter BF is then transmitted through the transmittin channel TL to the modulator-amplifier A Current of the oscillator 0 is also impressed upon the .modulator-amplifier MA current of this oscillator representing preferably an even harmonic of a fundamental frequency of oscillator 0 the frequency of oscillator 0 being preferably hi her than the frequency of oscillator 0 T e modulator-amplifier MA therefore modulates the signals originating in line L a second time and on a still higher frequency and transmodulation, upper and lower side bands of the frequency of the oscillator 0 may be transmitted to the band filter B F, each side b'and representing current coming in over one 'or" more of'the lines such as L, or L modulated upon the. current of the corresponding oscillators such as 0 or 0 respectively. The band pass filter B F may freely transmit the lower side bands resulting from the latter modulation. while substantially suppressing the carrier frequency, the upper side bands andall other products of modulation.

In accordance with this invention, the currents in each group which represent successive odd harmonics of a fundamental frequency are successively raised in the frequency spectrum as a result of modulation, so that t ese successive odd harmonics may assume positions in the frequency spectrum adjacent to each other. That is to say, the products of modulation of the .currents of group 2 are raised in the frequency spectrum as a result of modulation with current of the oscillator 0 so that the currents of group 2 may beelevated in the frequency spectrum with respect to the currents of group 1. -By so elevating the currents of each of the successive groups it is possible to simultaneously transmit these currents through repeating coil R and over the'main the lower, side bands of the currents'of oscillators 0 and 0 the stem may also be arranged so that the osclllators 0 and 0 transmit currents, the upper side bands of which may be similarly employed for transmission over a common transmission path such as ML,, without undue interferonce. It will also be understood that, while oscillators O and 0, have been referred to as oscillators of odd harmonics of a fundamental frequency and oscillators 0 and lator-amplifier D 0, have been referred to as oscillators of higher, even harmonics of the same fundamental frequency, it is within the sco'peof this invention tohave oscillators O and O transmit even harmonics of a fundamental frequency and oscillators 0 and O transmit currents which may be odd harmonics of the same fundamental frequency.

The bands of frequencies passmg band pass filter B,F at station A are transmitted through the repeating coil R at station-B, through the band pass filter B F to the demodulator-amplifier. DA Current of the oscillator 0, which sustains oscillations of .a frequency substantially equal to the frequencf of those oscillations sustained by the oscil tor 0,, at station A, is also transmitted to the demodulator-amplifier DA As a result of demodulation there appears in the out ut circuit of the demodua number of singly modulated currents substantially the same as the currents resulting from modulation at station A and assing the band filters BF and BF ese singly modulated currents are selectively transmitted by the band pass filter BF and BF,,, and are transmitted to the respective demodulator D,,' and D As a result of demodulation, the original signals are reproduced and are transmitted to the line L,,' and L res ectively.

ig. 2 shows a number of curves illus- .trating the principles of this invention.

Ten signaling sources are assumed to be resent in each group, the frequencies f, to 2 inclusive, being used for the first modulation of the currents of these sources, respectively. After the first modulation has been effected there are present a plurality of similar groups of currents each representing successive harmonics, preferably odd harmonies of some common fundamental frequency. The currents within groups 2 and 3 are then modulated a second time upon still higher frequencies which may preferably be even harmonics of the same common fundamental frequency, F and F, representing the frequencles upon which the currents within groups 2 and 3 may be respectively modulated. The band pass vfilters freely transmit the lower side bands resulting from modulation while substantially suppressing the "upper side bands. Thus, modulating the currents within groups 2 and 3 a second time it is possible to raise these currents in the frequency spectrum so that they assume positions adjacent to each other and to the position in the frequency spectrum occupied by the currents in group 1.

Fig. 3 shows how it is possible to use'directed radio beams in this invention to supplant the four-wire line circuits described hereinabove for transmission between two stations, such as A and B. ML and ML are comparatively short four-wire line circuits which connect one radio terminal to apparatus similar to that shown in Fig. 1 located at station A; ML, and ML, are four-wire line circuits which connect the other radio terminal to apparatus similar erate such a system with high efiiciency, it

may be found desirable to raise the frequencies of currents impressed upon the various lines by modulating these currents a third time upon still higher frequencies, all of which is within the scope of this invention.

By employing oscillators throughout the system which produce either odd or even harmonics of a common fundamental frequency, it' is possible to substantiall decrease'the interference and distortion introduced by such apparatus as loading coils, transformers; etc. It is well-known that such apparatus necessarily interposed in any transmission path introduce harmonics which frequently interfere with the faithful transmission of signals. By employing frequencies which simulate those introduced by the apparatus present in the transmission line it is possible to minimize the interfering 'and distorting e'fiectintroduced by such apparatus. r

While this invention has been shown and described in a certain particular arrange.- ment merely for the purpose of illustration, it will be understood that the general principles of this invention may be applied to other and widely varied organizations without departing from the spirit ofthe invention or the scope of the appended claims.

What isclaimed is:

1. In a system in which signals are to be transmitted substantially free from the distortion introduced by transformers, loading coils, and the like, the combination of a plurality of sources of low frequenc sig- 'nals, aplurality of low frequency osci ators low frequency signalin source, a pluralit of high frequency osci ators each of a di ferent even harmonic of the same fundamental frequency, one corresponding to each low frequency signaling source, means for beating the signals of each low frequency signaling source with the oscillations of a corresponding low frequenc oscillator, and means for beating the resu tant waves with the oscillations of the high frequency oscillator corresponding to the same sig naling source.

2. In a system in which signals are to be transmitted free from the harmonic distortion introduced by transformers, loading coils, and the like, the combination of a lurality of oscillators of successive odd armomcs of a fundamental frequency, a plurality of oscillators of successive even harmonics of the same fundamental frequency, a plurality of signaling sources, means for modulating the current of each of said odd harmonics by the signals originating in a predetermined number of said signaling sources, means for modulating-the modulated odd harmonics upon the currents of said even harmonics corresponding thereto, and a transmitting medium over which said doubly modulated signals may be transmitted.

3. The combination of a plurality of oscillators of successive odd harmonics of a fundamental frequency, a plurality of oscillators of successive even harmonics of the same fundamental frequency, a lurality'of signaling sources, means for mo ulating the signals ori inatin in a predetermined number of sai signa ing sources upon the currents of each odd harmonic, means for modulating a predetermined number of said modulated odd harmonics upon the currents of each of the even harmonics, a transmitting medium over which the signals thus doubly modulated may be transmitted, means for demodulating the plurality of doubly modulated signals with the currents of even harmonies employed in modulation so as to derive a lurality of odd harmonics modulated with said signals, said odd harmonics being substantially the same as those employed in modulation, and means for demodulating the plurality of modulated odd harmonics with substantially the same currents of the odd harmonics as were employed in modulation in order to derive the signals transmitted b said sources.

4. The com ination of a transmitting station comprising a plurality of oscillators of.

successive odd harmonics of a fundamental frequency, a lurality of oscillators of successive even armomcs of the same fundamental frequency, a plurality of signaling March 1927.

sources, means for modulating the signals originating in said signaling sources upon the currents of said odd harmonics of the fundamental frequency, a predetermined number of said signaling sources corresponding to the current of each odd harmonic, and means for again modulating the modulated odd harmonics of the fundamental frequency upon the currents of said even harmonics of the fundamental frequenc a predetermined number of said mod ated odd harmonics corresponding to the current of each even harmonic, and a receiving station comprising means for demodulatmg the lurality of doubly modulatedsignals with the currents of the same even harmonics employed in modulation at the transmitting station in order to derive a plurality of odd harmonics modulated I wit said signals, and means for detecting and deriving from the plurality of modulated odd harmonics the signals transmitted from the transmitting station by said. signalin sources.

.5. e combination of a plurality of groups of oscillators of successive odd harmomcs of a fundamental frequency, each group having substantially similar successive odd harmonic oscillators, a plurality of oscillators of predetermined fr uencies one corresponding toeach group, an means for beating all of the currents within the respective groups with the currents of the corresponding oscillators of predetermined frequencies so -as to produce-a plurality of grou s of frequencies one beside another in the requency spectrum. a

6. The comblnation of a plurality of groups ofsubstantiall equal successive odd harmonics of a fun amental frequency, a plurality of signaling sources one corresponding to each odd harmonic in each group, means for modulating the signals of each signaling source upon the current of the corresponding odd harmonic frequency, a plurality of oscillators of predetermined frequencies one corresponding to each group, and means for modulating all of the modulated currents of all the groups upon the currents of the predetermined frequencies, all of the modulated currents of any one group being modulated upon the current of only one of the predetermined frequencies, thereby producing a plurality of groups of signals adjacent to each other in the frequency spectrum.

In testimony whereof, I have signed my name to this specification this 30th day of FRED J. SINGER. 

